Doctors know that myeloma begins with one abnormal plasma cell in your bone marrow — the soft, blood-producing tissue that fills in the center of most of your bones. The abnormal cell multiplies rapidly.

Because cancer cells don't mature and then die as normal cells do, they accumulate, eventually overwhelming the production of healthy cells. In the bone marrow, myeloma cells crowd out healthy white blood cells and red blood cells, leading to fatigue and an inability to fight infections.

The myeloma cells continue trying to produce antibodies, as healthy plasma cells do, but the myeloma cells produce abnormal antibodies that the body can't use. Instead, the abnormal antibodies (monoclonal proteins, or M proteins) build up in the body and cause problems, such as damage to the kidneys.

A connection with MGUS

Multiple myeloma almost always starts out as a relatively benign condition called monoclonal gammopathy of undetermined significance (MGUS).

In the United States, about 3 percent of people older than age 50 have MGUS. Each year, about 1 percent of people with MGUS develop multiple myeloma or a related cancer.

MGUS, like multiple myeloma, is marked by the presence of M proteins — produced by abnormal plasma cells — in your blood. However, in MGUS, the levels of M proteins are lower and no damage to the body occurs.

Risk factors

Factors that may increase your risk of multiple myeloma include:

Increasing age. Your risk of multiple myeloma increases as you age, with most people diagnosed in their mid-60s.

Male sex. Men are more likely to develop the disease than are women.

Black race. Black people are about twice as likely to develop multiple myeloma as are white people.

History of a monoclonal gammopathy of undetermined significance (MGUS). Every year 1 percent of the people with MGUS in the United States develop multiple myeloma.

Reduced kidney function. Multiple myeloma may cause problems with kidney function, including kidney failure. Higher calcium levels in the blood related to eroding bones can interfere with your kidneys' ability to filter your blood's waste. The proteins produced by the myeloma cells can cause similar problems.

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